Forum Discussion

MEXICOWANDERER's avatar
MEXICOWANDERER
Explorer
Sep 21, 2015

Super Cap USB Charging Recharging (?)

I do not know as much as I should about "super caps". So I'll be safe here and play it dumb...

I've got a chance to get a quantity of 5.5 volt rated four point four Farad super caps.

I've got a bunch of gizmos that need recharging, like a smart phone, a Nook, you name it.

Could I get say three or four of the supercaps, parallel them for like 12 or 16 farads, then use a wire wound power resistor to control charging and recharging current between the supercaps and the gizmos?

I believe all the devices use the same technology lithium rechargeable battery but of course in different milliamp hour capacities.

Wirewound resistor or is there a better way to control current as far as versatility and efficiency is concerned?

All of this of course becomes academic if the caps cannot hold a charge for a couple of weeks (at least). Taking the extreme what is the milliamp hour ratio between say sixteen farads and one single Nook battery?

I can use the car lighter socket to fire up a DC to DC buck converter to whatever battery chargig voltage seems appropriate for the LiPo batteries.

But laying at the bottom of all this are so-called battery recharge packs with absurdly lying milliamp hour ratings. No way in hell is a twenty dollar eight ounce battery pack going to have 33-amp hours (33,000 mah) at 5-volts.

And I don't have the cash to buy a hundred dollar recharging pack. Going against me, is I have no idea how to measure 16-farads against howeversomany milliamp hours of battery pack.

Other than me whistling in the dark is my idea feasible or wishful thinking?

Thanks In Advance!!
  • MrWizard's avatar
    MrWizard
    Moderator
    Sep 21, 2015
    exactly
    thats why agree, with the use of the 13,000 MA battery module
    instead of super caps
  • LScamper's avatar
    LScamper
    Explorer
    Sep 21, 2015
    Here's the deal. My cell phone battery is rated at 2,800 mAh (2.8 Ah) at 3.85 V. Watt-hours equal Amp-hours x Volts, 2.8 x 3.85 = 10.78 Wh. To convert Watt-hours to Watt-seconds multiply by 3600. So 10.78 Wh = 38,808 Watt seconds, the total amount of energy stored in this fully charged battery. One Watt-second = one Joule. A Joule is the measure of energy. So the total energy stored in this battery is 38,808 Joules.

    Now for the 16 farad capacitor. Total energy stored in a capacitor is total Joules = (Volts x Volts x capacitance)/2. Total Joules = (5.5V x 5.5V x 16 farads)/2, total Joules = 242 Joules stored in this 16 farad capacitor.

    So the battery stores 38,808 Joules and the capacitor stores 242 Joules. Divide 38,808 Joules by 242 Joules and get 160.36.

    Bottom line is that the battery stores 160.36 times more energy than the 16 farad capacitor! Of note is that you will not be able to transfer all the 242 Joules from the capacitor to the battery.
  • MrWizard's avatar
    MrWizard
    Moderator
    Sep 21, 2015
    But if it will recharge your nook 5 times, per each one of its cycles
    .... that is 2500 recharges of your nook
    What is the Ma hrs of the nook battery or the phone battery
    My neighbors T-Mobile flip phone has an 850ma battery, that pack could recharge it 14 times
    He just ordered a new battery
    My Samsung S4 came with a 2600ma battery, the would be 5 phone recharges, before the pack needed to be charged
    And I bought an oversize extended 5600ma battery with new back , for it
    The HTC Incredible setting here on the table, uses a 1300ma battery
    That pack would charge it 10 times, then recharge the pack
  • MEXICOWANDERER's avatar
    MEXICOWANDERER
    Explorer
    Sep 21, 2015
    accsys wrote:
    Mex, the technology is changing rapidly. Just a couple of years ago an emergency starter pack (like the one I currently have) weighted 20 pounds and worked remarkably well. The current ones are only half the size and do the same thing. Likewise I believe the device chargers are in a major time of downsizing and increase in abilities. This cheapie at Solid Signal doesn't purport the outrageous capacities you alluded to but still is a lot of energy for a small package.


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    But thanks for the link. Now, your site looks rational. I guess 500 charges is all they're good for. Was hoping for a non existent miracle.
  • MrWizard's avatar
    MrWizard
    Moderator
    Sep 21, 2015
    Here is instructions on building a rechargeable battery replacement with 400 farad caps
    Instructable

    Read up, should give you some good info
  • accsys's avatar
    accsys
    Explorer
    Sep 21, 2015
    Mex, the technology is changing rapidly. Just a couple of years ago an emergency starter pack (like the one I currently have) weighted 20 pounds and worked remarkably well. The current ones are only half the size and do the same thing. Likewise I believe the device chargers are in a major time of downsizing and increase in abilities. This cheapie at Solid Signal doesn't purport the outrageous capacities you alluded to but still is a lot of energy for a small package.
  • MEXICOWANDERER's avatar
    MEXICOWANDERER
    Explorer
    Sep 21, 2015
    I was afraid this was a wild lithium chase right from the start. Thank you Mr. Wizard. I could limit current with a high-enough value resistor at the expense of eating cap charge wattage potential. But seeing those freakin' ridiculous ching-chong ads promising jumpstart wattage from a thirty-dollar wallet-size packet just gets my goat.

    Maybe this heat is scrambling my brains. Maybe what I -should be- looking for is a top-notch car cigarette lighter charger. One that can support simultaneous 2-amp charges (4-5 amps total).
  • MrWizard's avatar
    MrWizard
    Moderator
    Sep 21, 2015
    There are some YouTube videos showing guys powering tv, radio game etc from super caps, this only lasts a few minutes
    I don't remember the number of farads involved, but I'm thinking they did them in 9v and 12v configurations

    So far the conclusions I remember, were great for engine starting OR surge support on inverter systems, useless as stand alone battery replacement, they don't have the amp hrs
    Check them out before investing time in this
    And I don't think a wire wound resistor would work anyway
    It won't control the current surge, you would still need a USB charger in between the caps and the device, or you blow might those lithium batteries

    As far as holding the charge, the guys using them for engine start seem happy, but I don't remember anybody saying they left the car parked for weeks

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